Recording instrument mechanism



Dec. 19, 1950 H. L BowDlTcH nEcoRDING msmuun'r uEcmNIsu 2 Sheets-Sheet 1 Filed Oct. 18, 1949 INVENTOR. #0.a 50k/.wmv

Dec. 19, 1950 H. L. BowDlTcH RECORDING INSTRUMENT IIECHANISI 2 Sheets-Sheet 2 Filed Oct. 18, 1949 JNVENToR. @Wa/76H A/oez Z,

m2, zw@ qw Patented Dec. 19, 1950 i UNITI-zn STATES PATENT. orrlcs 2.514,56 RECORDING INSTRUMENT MECHANIS! non L; navman,

Foxboro. Masa., assigner to The Foxboro Company, Foxboro,

Mass.

Application October 18. 1949, SerialNo. 122.021

` lclllln. (Cl. 348-112) verting rotary movement' of a condition-responsive mechanical member into a corresponding straight-line movement oi' a recording element.

or ilow may be used. The reactions of the sensing device to variations in the value of the variable condition, e. g., temperature, are transmitted by liquid or gas pressure or an electric current to the instrument proper, wherein they are normally converted into rotary movement of a mechanical member. This rotary movement is linear with respect to variations in the value of the variable condition. (The term linear" is used here and elsewhere in the present specification in its mathematical rather than its physical sense to denote that the extent of angular movement of the rotatable mechanical member is linearly proportional to changes in the value of the measured condition.)

^` In instruments of the type referred to, it is sometimes desirable to record the value of the variable condition on a so-called strip chart. i. e.,

a paper recording surface that `travels in a' straight-line path past a recording element which may be i'or example, a 'Il ie recording lement normally moves transversely with respect 'to the'path of movement o! the chart `to record the values of the condition. In such cases, it is desirable that the recording element have a straight-line motion corresponding to the rotary movement of the above-mentioned mechanical member. which in turn, moves in response to variations ln the measured condition. Moreover, the movement oi the record element should be "linear" with respect to the rotary movement of the mechanical member.

various mechanisms have been used with strip -ohart instruments. One of these produces a swinging, arcuate recording movement directly from the rotary movement mentioned above. This is unsatisfactory because it. produces a curved record line which is diiiicult to interpret because of its departure from straight-line coordinates. In another structure, the rotary movement causes a carriage to be moved across the instrument in a straight-line movement. This structure is undesirable because it is cumbersome and expensive.

Accordingly, it is an object of the present invention'fto provide, in instruments of the type res ferred to, new and improved mechanism for con-1 the condition-responsive member;

It is another object of the invention to provide mechanism oi' this character which produces not only straight-line movement of the recording ele'-l ment but also causes the recording element move`- ment to be maintained in substantially linear relation with respect to the rotary movement of Other objects of the invention will be in part obvious and in part pointed out hereafter.

As an illustrative embodiment of this invention, mechanism is shown in the accompanying drawings and described herein in association with a strip chart type of recording instrument. With thismechanism, the rotary actuating movement which is mentioned above may be readily, simply. and inexpensively converted to straight line recording movement which'is linear with respect to the rotary movement.

In the drawings:

Figure I is a schematic illustration of an ap-` plication of a strip chart instrument to a process requiring temperature control;

Figure II is an illustration in perspective of a mechanism embodying this invention and oper able as a part of av strip chart recorder, such `as thatshowninll'igurenand y Figure III is a schematic illustration oi the structure of Figure II, in association with a strip Referring to the temperature control process arrangement shown as Figure I, at the lower left thereof, there is a tank i0 containing a liquid i'l which is to be maintained at a desired temperature. 'I'he right wall of the tank is penetrated by a steam inlet pipe i2 through which steam ii passed into the liquid il in a controlled manner depending upon the entire arrangement, as will be seen, to maintain the liquid at a desired tem# perature. 'I'he left wall of the tank it has, extending therethrough and into the liquid a thermometer Il of the type which produces vapor pressure variations in accordance with temper'- ature variations. and there is a connection between the thermometer and the centrally located strip chart recording instrument Il, in the form of a small tube I5 through which the vapor pres# sure variations from the thermometer Il are transmitted. Leading into the left side 'of the instrument, below the small tube II, is an inlet It for supplying the air under pressure neces'- sary to operate the instrument i4. Leading out of the right side of the instrument is an output pipe I1 through which pneumatic control prelsures from the instrument are transmitted The pipe I1 is connected, at the right of the instrument, to an air operated valve Il in the steam pipe l2. Thus the instrument controls the steam valve is in accordance with the temperaturc of the liquid Il.

In this instrument, as in those previously generally mentioned herein, vapor pressure variations from the thermometer result in rotary movement within the instrument, which in this instance is the movement of a rotary shaft as indicated in Figure II at the bottom left by the number II and in Figure III at the top left by the same number. Associated with the showings of the rotary shaft il are double arrows indicating that the shaft may rotate in either direction. depending upon whether the vapor pressure variations from the thermometer il indicates a risc or fall in the temperature of the liquid Il.

Referring now to Figures II and III, the mechanism operable by the rotation of the shaft il is shown by itself in Figure II, and in a more schematic manner, in the upper portion of Figure III. the lower portion of Figure III being a showing of a strip chart 2l in association with the mechanism. `-Thus the mechanism is located above the strip chart and in laterally central location with f respect thereto.

It will become apparent from the following description that essentially, the action of this mechanism is to swing a recording arm about a pivot, the normal result of which would be to swing the recording end of the arm in an arc. and to simultaneously move the pivot bodily in an arc in opposition to the no1-mal" arc to produce a resultant straight-line recording movement.

'I'hc present mechanism is actuated by rotary movement of the shaft il corresponding to temperature variation in the liquid il. This rotary movement is transmitted to another shaft, centrally located, Figure III, at the bottom of the mechanism, as indicated by the number 2 I. 'I'hese shafts are parallel, and are connected to each other through the arms 22 and 2l which are nxed respectively to the shafts I and 2i. and a link 2l which connects the arms 22 and 2l. 'I'hese arms are each provided with a series of connection openings 28, in order that the rotational relation between the shafts I9 and 2| may be varied by connecting the link 24 at different openings in the-arms, to vary the operating lengths thereof and consequently the leverage. Connecting link 2l to diiferent openings in arms 22 and 2l changes the amount that one shaft rotates for a given movement of the other shaft, but does not change the linear relation between their movements. and consequently the rotation of the shaft 2| is also linear with respect to the thermometer variations.

A further adjustment is provided, see Figure IL between the arm 2l and the rotatable shaft 2| to which it is secured, in the form of a screw and gear sector unit on the shaft 2| at the point of connection of the arm 2l thereto. as indicated at 2l. This unit may be used to adjust the arm 23 about the shaft 2| as a center to vary the rotary of the shaft 2| with respect to that of thcshaft Il, or to adapt the arms 22 and 2l to a longer or shorter link without changing the relative rotary positions of the shafts Il and 2|.

On the forward part of the shaft 2|, the pivoted arm 21 is mounted for movement therewith, being xcd thereto by a set screw 2l. Referring to Figure III. this arm 21 extends upwardly away from the strip chart 2l, and its movement, as controlled by the rotation of the actuating shaft Il. is arcuate and of the order of degrees, that is. about twenty-two and one-half dmzes on either side of a vertical center line extending transversely through the pivot shaft 2|. The arm 21 is shown, in Figure III, in full lines at its laterally extreme left position A. andin dotted lines at its central vertical position 3, and at its laterally extreme right position C. As -best seen in Figure II. the outer end of the arm 21 is bent back on itself in U formationI with a pivot shaft 2l extending between the legs of the U as the pivot support of the bell crank lever Il, as well as its connection to the arm 21. Thus the bell crank pivot shaft 2| is located at a substantialy distance from the pivot 2| of thearm21.

The bell crank lever I0 is formed with a long, recording leg li extending from the bell crank lever pivot connection 2|, down over the chart 2l, and a short. cam leg I2 extending generally to the right from the pivot 2l, with these legs at right angles to each other. The pivot 2U is parallel to the previously mentioned rotary shafts Il and 2i, and perpendicular to the recording face of the strip ehm an, so that the am a1' and the bell crank lever Il swing in parallel planes. which are also parallel to the recording face of the chart. The free end of the recording leg Il of the bell crank lever swings over the upper portion of the chart and, Figure II, a pen is mounted thereon at Il, for recording, on the chart, the movements of the leg ll across the chart.

In Figure III, the straight line movement of the end of the recording leg 3l is illustrated by showing the chart as being stationary. and the three positions A, B, and C of the arm 21 locate the free end of the recording leg Il in three positions across the chart, with the line between the three positions on the chart indicated at Il as representing the straight line movement. As shown on the chart in Figure I, the record line is a combination of the transverse movement oi the pen Il and the downward movement of the strip chart 20. Secured to the recording leg of the bell crank lever as a visual indication of the lateral position of the pen I3 on the chart, is a target member shown in Figure I1 only, at Il.

At the right of the mechanism, Figure III, as a means of aiding in rotating the bell crank lever il on its pivot 29, the cam plate 36 is provided. the upper edge thereof being formed as a cam track 21. This cam plate is mounted above the strip chart and parallel with the recording face thereof, and, as a convenience in this instance, the lower left portion of the cam plate provides one of the bearings for the pivot shaft 2|. The free end of the bell crank lever cam leg I2 is provided with a cam contact roller ll for engaging the cam track I1. This roller is heavy enough to oiIset the weight of the bell crank recording leg `2i and keep the roller in contact with the cam edge 21.

'I'he curve of the cam track depends onrthe dimensions chosen for the various parts of the mechanism. Not only must the record line be straight, but the movement cf the pen Il therealong must be linear with respect to signals from the thermometer. Proper formation of the cam track contour balances the straight-line facfor against the linearity" factor to produce a combination of both in the movement of the pen.

chart 2l and its associated mechanism is standard practice. There are upper and lower rollers, I9 and l0, with the chart being drawn from one to the other. usually downward, so that the record remains visible for some time after it has been made, before it is hidden by being rolled up on the lower roller. Such a record may be seen in Figure I. g

As the arm 21 is moved about its pivot 2| by a change in thermometer signal, the bell crank lever It is moved bodily therewith, tending to move the free end of the bell crank recording leg ll in an upward arc. However, at the same time, the movement of the bell crank lever cam leg 32 along the cam track 81 causes the'bell crank lever to move about its pivot 29, introducing a tendency to move the free end of the leg 3i in a downward arc. 'I'he resultant of these two tendencies is straight-line movement of the pen 3l across the chart I9. as indicated by the line 34.

'Ihe choice of dimensions for the various parts of the mechanism, for example, the length ot the arm 21, and the lengths of the legs ofthe bell crank lever, are chosen with an eye to the desired relative locations of the mechanism and the strip chart, and the amount of motion desired. Any combination of lengths and 'positions of leversand arms such as shown and described herein, which balances one arcuate movement against another to provide a straight line movement, is believed to be within the scope of this invention.

The mechanism of this invention is not only simple, inexpensive, and productive of a straight line movement, but it also has the further conit can be used to readily and simply adapt the actuating mechanism which produces rotary movement in standard rotary operating instruments, to instruments requiring a straight line recording movement, such as strip chart instruments.

A mechanism for converting angular movement to straight line movement for instruments of the type used for recording, indicating, or controlling values of variable conditions such as flows, pressures, temperatures and the like, in which equal angular movements produce equal straight line movements, said mechanism comprising the novel combination of a pivoted arm, movable about its pivot through an arc of the order of 45 degrees,

. a bell crank lever pivoted on said arm for bodily movement therewith, a cam mounted for operative relation with one leg of -said bell crank lever, and a pen mounted on the other leg of said bell crank lever, -whereby as said arm is moved about its pivot, said bell crank lever is pivoted with respect to said arm as a result of the cam leg of said bell crank lever following said cam, and the pen on the other leg of said lever describes s aid straight line.

ille of this patent:

UNITED STATES PATENTS Number Name te siderabie advantage that. bewust 0f thee fvwm. 35 3,442,536 clark .mulig 1, 194g 

